Originally Posted by
operator
The OP doesn't say that. I imagine he'd be talking about levers + shifters combined. And you're wrong about the levers. You need cantilever compatible brake levers if he is to convert. The majority of flat bar levers will be for linear pulls.
For a bike from the 1970s, maybe the best choice would be some vintage levers. I don't know but I believe the calipers were much the same for the upright and drop bars. Besides, if he scored a set of vintage levers on ebay, they would have a period-correct look which matched the bike.
To the OP, by cable ends I mean the piece of alloy which is cast onto the end of the cable. It is what fits into the brake lever and gives it something to pull against. Some are shaped like a banjo, some are shaped like a potato masher, and there are different sizes.
You might get more help on the classic and vintage forum, though I bet many of its readers also check out this forum. I am not absolutely positive when Motobecane switched to the standard 25.4 bar clamp dia, which was then changed to 26, then 31.8, but someone there would know. They could probably also tell you what your chances were of finding an old, French size, upright handlebar.
Before you spend too much, maybe check out some nice Japanese or Taiwanese mixtes. They might come with the bars you want, and would be easier to change over in case they came with drop bars, and you could probably sell the Grand Jubilee to someone who would appreciate its oddities instead of decrying how inconvenient they made modification.